This invention relates to a compact gas turbine engine propulsion simulator and, more particularly, to a miniaturized turbomachine in which a pneumatic energy supply system replaces the conventional fuel-fired combustor of a gas turbine engine and which is capable of accurately reproducing the in-flight aerodynamic characteristics of a wide range of gas turbine engines and gas turbine engine cycles when installed in an aircraft model during wind tunnel testing.
It has long been the accepted practice of the aircraft industry to simulate the in-flight performance characteristics of aircraft by testing scale models in wind tunnels. In this manner, the design and development cost and time are significantly reduced. However, there has historically been a great deal of difficulty in correlating full-scale aircraft data with scale model wind tunnel data due, largely, to the inability of an unpowered model to simulate simultaneously all of the complex flow interactions between the aircraft structure and its power plant. In the case of gas turbine engine (turbojet or turbofan) propulsion, this was true regardless or whether the engine was mounted externally, as on a pylon, in a pod, or internally of the aircraft. However, several years ago an important innovation occurred in propulsion simulation for scale model wind tunnel testing with the introduction of the simulated reaction engine model described in particularity in U.S. Pat. No. 3,434,679, issued to John T. Kutney et al, and which is assigned to the assignee of the present invention.
This model, for the first time, provided the basis for simulating the in-flight aerodynamic characteristics of a subsonic, high bypass, fan-type gas tubine (turbofan) engine in a subsonic wind tunnel aircraft model. Basically, the external configuration of the simulated engine model was sized and reduced by a linear scale of the engine simulated, while the fan and turbine were sized to develop a pressure ratio across the fan substantially similar to the pressure ratio across the simulated engine fan and a mass flow rate reduced in relation to the mass flow rate of the simulated engine by substantially the square of the reduced linear scale. For subsonic turbofan propulsion simulation, such as characterizes current wide-body commercial aircraft, this technique now enjoys industry acceptance. However, as successful as the simulator of Kutney et al has been, it has not proven entirely adequate for propulsion simulation of internally or pod-mounted gas turbine engines for supersonic, fighter-type aircraft characterized by afterburning (reheat) or non-afterburning (dry) operating modes. For this type of wind tunnel program, three tests must still be conducted in an attempt to achieve realism. First, the aircraft model is tested in a flow-through mode wherein the incoming engine flow is permitted to enter the inlet and flow through the model. However, in order to vary inlet flow over the required range, the aft end geometry must be distorted. Next, the jet-effects mode correctly simulates the aft flow field only. Here the inlet is faired over, diverting all of the flow around the model. High pressure air is introduced and then exhausted through the correct nozzle geometry at the required nozzle pressure ratio. Finally, an additional test to obtain isolated inlet performance has also been found to be necessary. The results of these three tests are then combined analytically without accounting for simultaneous interactions of the forward and aft flow fields or model-to-model geometry differences.
The problem now confronting the test engineer is how to simulate the wide range of propulsion flow fields and complex flow interactions in wind tunnel model aircraft testing required of a truly integrated model aircraft and propulsion system. In particular, what is needed is a propulsion simulator having multimission operational flexibility (i.e., capable of simulating a wide range of engine cycles) in order to model increasingly sophisticated engine installations with complex aircraft/engine interactions and integration problems. Preferably, the simulator must be capable of simulating a wide range of engine types and cycles with a single, standard basic gas generator which is readily comformable to particular test aircraft requirements. Furthermore, the tight constraints on space in aircraft wind tunnel models dictate that the simulator be extremely compact in order to avoid compromising the aircraft envelope in order to accommodate the propulsion simulator.